This invention generally relates to a power controller for a transmitter of a digital or analog process control device.
Industrial control systems have evolved into complex computer-controlled networks that facilitate communication and control among, for example, one or more central control interfaces and field devices. A central control interface can be used to coordinate communications and control of an entire process, or it can be used to control a portion of a larger, distributed computerized process control system. In some cases, the process field devices and related machinery (e.g., pumps, valves and heaters) that form the process control system can occupy spaces large enough to be measured in square miles. Accordingly, the field devices and machinery require highly integrated control.
Generally, field devices are used to monitor the process being controlled, and to provide feedback for and adjustment of that process. Field devices also may be used to control the entire process and coordinate communications, without a central control interface/station. Field devices may include sensor-type field devices for sensing variables of a process, or control-type field devices (e.g., positioners and actuators) for controlling parameters of a process. Sensor-type field devices such as temperature sensors and flowmeters measure process variables and may communicate their measurements to the central control interface for monitoring and possible process adjustment. Control-type field devices such as pumps and valves may be controlled by the central control interface, or a control-functioning field device or devices, in real time to adjust control of the process. The adjustment of the field devices may be automatically controlled by a computer running process control software, or manually controlled by, for example, process engineers and factory personnel.
In many cases, field devices and central control interfaces communicate with each other using a communication network, such as a local area network (LAN). Generally, each device (field devices and central control interfaces) connected to the communication network includes a transmitter for sending and receiving data in the form of electrical signals. These signals, depending on the communication network, can include, for example, analog, digital and pulsed signals. The communication network may be used to transmit control signals and sensor signals among the various components of the process control system. Furthermore, the communication network facilitates monitoring and diagnostics of the process control system components and the process itself.
Various aspects of the process control system may follow a proprietary protocol or may follow a widely-accepted standard developed by process control industry participants. These protocols/standards may specify process control system parameters such as communications protocol (e.g., bit rate of data transmission), power consumption, length of the communication bus, and safety measures. These protocols/standards provide many benefits for process control systems including coordination of field devices, safety provisions, and, in the case of widely-accepted standards, compatibility and interchangeability of components.
In one implementation the process control instrument includes a sensor/actuator portion and a transmitter portion connected to the sensor/actuator portion and operable to communicate with other process variable transmitters through a communication network. The transmitter may include a processing module and a power module operable to generate a power output supplied to at least the transmitter portion, wherein the power module is operable to adjust the power output based on a power control signal. Moreover, the power control signal may be generated by a controller device remote from the process control instrument and communicated to the process control instrument over the communication network. The power output of the power module may be an electric current supplied to at least the transmitter portion of the process control instrument.
Additionally, the power module may include a power control module for adjusting the power output. This power control module may include an amplitude limiter operable to limit a power input to the process control instrument according to a controllable amplitude limit, and a power rate of change unit operable to limit a rate of change of the power input to the process control instrument according to a controllable adjustment rate limit. The controllable amplitude limit may be automatically controlled by software and/or circuitry, and/or controlled by human intervention. Also, the controllable adjustment rate limit may be automatically controlled by software, human intervention, and/or circuitry. Furthermore, the controllable adjustment rate limit may equal 1 mA/ms.
In addition, the communication network may include a hard-wired communication pathway operable to supply a bus power to the power module, and the power module may use the bus power as a source for the power output. The hard-wired communication pathway may be configured in a bus-with-spurs topology, a daisy-chain topology, a tree topology, and/or a point-to-point topology.
In another implementation, a process control system may include process control instruments, each of which may include a power control module that controls an available power level for the process control instrument, wherein the power control module is operable to adjust the available power level based on a power control signal. The process control system may further include a communication network electrically connected to the process control instruments and operable to conduct communication signals among the process control instruments, and a power supply operable to supply power to the process control instruments through the communication network. Further, the power controlled by the power control module may be electric current.
The process control system may further include a control station operable to generate the power control signal and control power distribution among the process control instruments. The control station may be further operable to determine power loads of the process control instruments and distribute functions among the process control instruments to balance the power loads of the process control instruments. Moreover, the control station may distribute functions among the process control instruments to balance power consumption among at least one of individual process control instruments, groups of process control instruments, and segments of the communication network. Also, the control station may be further operable to control power distribution of a limited quantity of power among the process control instruments.
In addition, the power control module may include an amplitude limiter operable to limit the available power level of the process control instrument according to a controllable amplitude limit, and a power rate of change unit operable to limit a rate of change of the available power level of the process control instrument according to a controllable adjustment rate limit. The controllable amplitude limit may be automatically controlled by software and/or circuitry, and/or controlled by human intervention. Also, the controllable adjustment rate limit may be automatically controlled by software and/or circuitry, and/or controlled by human intervention. Moreover, the controllable adjustment rate limit may equal 1 mA/ms.
Additionally, the communication network may include a hard-wired communication pathway operable to supply a bus power to the power control module, and the power control module may use the bus power as a source for the available power level. The hard-wired communication pathway may be configured in a bus-with-spurs topology, a daisy-chain topology, a tree topology, and/or a point-to-point topology.
One particular implementation of a method for managing power of a process control system may include determining initial power requirements of power-consuming functions distributed among process control instruments, which are electrically connected together by a network. The method may further include determining initial power loads of the process control instruments, and determining an available power level supplied by a power supply connected to the network. Also, the method may include distributing the power-consuming functions among the process control instruments, based on at least one of the initial power requirements, the initial power loads, and the available power level, to balance the power loads among the process control instruments. Distribution of the power-consuming functions among the process control instruments may be achieved using a control station connected to the network.
The process control system power management method may further include determining line losses of network branches connecting the process control instruments. Moreover, distribution of the power-consuming functions among the process control instruments may be based on the line losses of network branches.
Additionally, distributing the power-consuming functions among the process control instruments may include producing a balance of power loads with respect to individual process control instruments, producing a balance of power loads with respect to segments of the network, and/or producing a balance of power loads with respect to a limited amount of power supplied by the power supply.
Another implementation of a power management method of a process control system may include determining initial power requirements of power-consuming functions distributed among process control instruments which are electrically connected together by a network, determining initial power loads of the process control instruments, and determining an available power level supplied by a power supply connected to the network. The power management method also my include controlling power control modules associated with the process control instruments, based on at least one of the initial power requirements, the initial power loads, and the available power level, to adjust a power level available to individual process control instruments and balance the power loads among the process control instruments. Control of the power control modules associated with the process control instruments may be achieved using a control station connected to the network.
The process control system power management method may further include determining line losses of network branches connecting the process control instruments. Moreover, control of the power control modules associated with the process control instruments may be based on the line losses of network branches.
Additionally, control of the power control modules associated with the process control instruments may include producing a balance of power loads with respect to individual process control instruments, producing a balance of power loads with respect to segments of the network, and/or producing a balance of power loads with respect to a limited amount of power supplied by the power supply.
Accordingly, the process control instruments can be used with various standards/protocols of the process control industry while realizing improved coordination and control of the process control instruments with respect to, for example, power limitations specified by the standards/protocols.
The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features and advantages will be apparent from the description and drawings, and from the claims.